Unlike other RTS games, scouting here is very important, as it stops you wasting units and allows you to prepare for a fight, or kill a small enemy group before they are ready. Using advanced radar or simple radar is a way of scouting,but sight via units is more accurate as it doesn't have radar wobble. Those that cloak (Infiltrator/Flea) are better as they are invisible and can close up on an enemy base and not be spotted.